Over half of all U.S. citizens will be exposed to a potentially traumatic event (PTE) during their lifetime. The recent, unprecedented man-made and natural disasters of 9/11 and Hurricane Katrina catastrophically illustrate that lifetime trauma exposure rates are rising. The psychiatric response associated with traumatic exposure involves post-traumatic stress disorder (PTSD), substance-use disorder (SUD), or co-occurring psychopathology (i.e., PTSD-SUD). However, not all individuals will develop psychiatric disorders in response to PTE exposure, underscoring the question: What are the factors that lead some individuals who are exposed to traumatic events down the path to resilience and other individuals down the path to risk for these disorders? This question can be examined effectively in a sample of firefighter (FF) recruits who will experience life-threatening events on a day-to-day basis as a result of their profession. FFs exposed to PTEs may follow a number of pathways towards pathology or wellness. Unfortunately, the variables and parameters that predict risk and resilience for PTSD, SUD, and PTSD-SUD symptoms and diagnostic caseness, as well as the patterns of recovery and relapse related to these disorders, are not well understood. In the proposed study, 400 urban, professional FF recruits will be followed from selection and training, through their early careers as FFs in a prospective, longitudinal evaluation. Resilience to, or development of, PTSD, SUD, or PTSD-SUD will be examined, as well as temporal patterns of symptom expression, recovery, and relapse. Biopsychosocial variables that influence post-exposure pathways and increase or decrease the likelihood of developing PTSD, SUD, or PTSD-SUD symptoms and/or caseness will be evaluated. Following a multi-dimensional pre-employment baseline assessment (i.e., genetic markers, family history, personality factors, prior PTE exposure and substance use), PTSD and SUD symptomatology plus empirically-derived predictor variables (i.e., trauma characteristics, acute peritraumatic responses, coping, and social support) will be measured at 3-month intervals for 3 successive years. Latent growth curve analyses, structural equation modeling, multigroup structural equation modeling, and cross-lag panel analytic approaches will test temporal dependency as well as postulated relationships between risk and resilience factors. This application is the next step in our research team's programmatic investigation of trauma-related disorders among FFs, with an emphasis on factors that may inform prevention and treatment guidelines for both FFs and other trauma-exposed populations. The long-term goal of this study is to build a FF database from recruitment through retirement in order to identify patterns of risk and resilience in this highly-exposed, essential public safety population.